The separation of water from hydrocarbons and/or halogenated hydrocarbon contaminates found in chemical industrial waste or from gaseous hydrocarbons generally requires a separation system capable of prolonged exposure to hydrocarbons without chemical degeneration or fouling. The allowed copending patent application Ser. No. 194,984 to applicant, filed May 17, 1988 discloses a method for drying a wet stream of hydrocarbon gas by the use of hollow fiber membranes while producing a hydrocarbon free water permeate. The method employes as a membrane, a nonporous self-supported hollow fiber membrane module, the membranes consisting of cuproammonium cellulose hollow fibers. A wet hydrocarbon gas stream is conducted into contact with the outside of the fibers and water is osmotically imbibed independently of convective pressure of the stream of gas from the stream into the fibers while preventing imbibing or permeation of the hydrocarbons and/or halogenated hydrocarbons. The water free of the hydrocarbons and/or halogenated hydrocarbons defuses to the bores of the fibers. The imbibed water free of the hydrocarbons and/or halogenated hydrocarbons is removed from the inside of the bores and the dry gas is removed from the outside of the membrane. The apparatus provides the ability in a process to osmotically imbibe water independently of convective pressure of the stream of gas from the stream into the fibers while preventing imbibing or permeation of hydrocarbons and diffusing the water free of hydrocarbon to the bores of the fibers.
The aforementioned process can utilize a sweep stream of dry air flowing within the bores of the hollow fibers which carries away water molecules as they appear on the inner surface or wall of the membrane fibers. Water immerging on the inner wall of the fibers is continuously removed by the sweep stream. Thus, the membranes are diffusion means consisting essentially of unsupported, nonporous cuproammonium cellulose having continuous uninterrupted services. The sweep stream provides water removing means for driving the diffusion dynamics and essentially drying the gas retentate. The sweep stream, acting as the water removing means, in combination with the ultra thin cuproammonium cellulose membranes and the unobstructed nonporous membrane surface, provide significantly improved results in separation dynamics when compared to prior art systems.
It is desirable to increase the efficiency of the aforementioned systems while decreasing the cost of the operation. One source of cost is the continual use of dry air from a dry air source for providing the sweep stream. The present invention provides means for increasing the efficiency of the inventive apparatus for drying the wet gas stream and lowering the cost of the operation of the same while not at all decreasing the capacity or capability of the apparatus.